1. Field of the Invention
The present invention relates to a reperforable BRIDGE PLUG of the type used for sealing in transitory or permanent form the perforations lined with pipes or tubes of insulation particularly those that are used in oil wells or the like.
2. Description of the Prior Art
The principal object of the invention is to obtain a new type of plug of the above mentioned type, adapted to be installed in the selected place by any of the proceedings or equipment used in the industry, either with the use of cables or tube lines for such purpose.
The invention has been made to considerably reduce the working and writing time of the costly equipment used in the art, resulting among other bentfits, that shall be enumerated in the course of this specification, in the elimination of the first gate pass prior to the installation of the plug and less time in the milling of the same for its destruction, because with the invention, its rotation has been avoided, through the turn interlock provided. With the above mentioned purpose in mind, the invention also contributes a remarkable constructive simplification that brings about an important economic advantage, and at the same time its technical improvements not only offer a better mechanical fastening, but the possibility of being used in various applications with the same structure, through the change of a single key piece. It is well known that a variety of plugs have been created with the purpose of sealing oil wells, according to the known manner of operating in this activity. Among them is a plug used as support of the sealing elastic body, a gasket composed by one or more deformable plug rings that are accomodated or adhered to the walls of the jacket pipe with the compression set effected by the displaceable pieces proper of the plug, in the inherent process for its placement, so the resilient material or rubber that constitutes the elastic body, does not unduly flow or become exhausted through the plug contour and effect its closing.
In other kinds of plugs, these annular bodies have been substituted, through both simple or double laminar washers, with a skirt of frusto-conical shape directed toward a conformation similar to the elastic body in agreement with the washers.
In other cases the sealing element is materialized by resorting to two or three independent elastic bodies, with peripheral lips and forms as displaceable blades, that complement each other with the purpose of improving the closure.
Other small differences existing among the known models could be mentioned. Notwithstanding, it is advisable to understand that the whole of these appliances resort to the use of two jaws arranged with the other component pieces at each side of the packers elastic body or bodies.
As known by the expert on the subject, these jaws, at the end of the process of placement of the plug, that is to say, once the expansion of the elastic packer body is obtained and the respective fuse pins are broken and before the weak tension point is broken, the above mentioned jaws, are expanded, nailing their teeth on the tube line of jacket pipe to secure the immovability of the plug in its position. In the already mentioned conventional plugs provided with two jaws, it has been proven that in the process of the plug fastening it is required that the indented jaws are approached between each other in order to provoke the deformation of the flexible gasket. Breaking the first fuse pin displaces the upper cone and the respective jaw, while the lower one remains fixed, so that relative displacement causes a strong rubbing of the teeth of the jaws against the steel tube wall which, taking into consideration the important forces in operation, the teeth suffer a strong abrasion making them blunt and subsequently restricting their capacity of penetration in the wall and therefore weakening the mechanical fastening of the plug. In some cases, both jaws are displaced impairing the situation.
Another constructive aspect of this pair of jaws may be mentioned, in certain cases they are constituted by independent segments fastened by "fuse" screws to the respective cone or maintained in position by rings mounted in a perimetral throat or by a wire of copper winding.
In another embodiment, the jaws are substantially cylindrical bodies with channels arranged according to interior generatrix which defines areas of lower resistance, but offer the problem of the formation of burrs in the fracture areas directed toward the periferic contour and moveover to the loosening of fragments the presence of which between the teeth of the jaws cause subsequent disturbances.
Other usual problems in the perforations under consideration are included in the rubbish found inside the tubes. In order to eliminate this, the use of baskets must be resorted to, incorporated with the gages for their recuperation, by passing this device through the tube line, so that all the matter that is found in its downward direction is collected in its interior basket. In the hitherto known techniques, the use of the gage is essential, in as much as with them there are found variations in the diameter of the jacket pipe. Variations may be originated, for example, in the perforated layers, that a mentioned above offer holes with burrs which may create problems in the downward direction of the plug. With the gage, collapses and/or failures are also detected which are due to an excessive thread of the pipe section, which also causes burrs in the edges of the pipe and even its flare shape. There are known the anomalies which may be found in the tube line covering the wells, that can be detected by the different systems used by the surface installations for placement of plugs.
It is obvious that taking into consideration the high cost of the equipment placed on the well, the less intervention time of each one on each perforation may result in a lower cost per cubic meter of the oil obtained. For such purpose it is very important to attain the maximum guaranty that the tube line with which the perforation has been lined be in perfect condition. That is to say, that since a slight diameter difference exists between the plug and the tube, the plug may be lowered without trouble and there are no undesirable burrs, collapses or rubbish which may affect its downward movement. Consequently, it is required to lower in the first place a calibrator device which carries downwardly all the rubbish which is being housed in its interior part. This kind of basket is exteriorly shaped, with annular calibrated bands the diameter of which will guarantee that the minimum diameter found in the well, shall not affect the lowering of the plug.
So in each perforation and in a manner prior to the placement of each plug, it is necessary to effect a stroke with the above mentioned calibrated basket. As briefly mentioned in the foregoing paragraph, the plugs may be fastened through arrangements operated by cable or pipe, in the first case the fastening system operated by remote control depends from a cable and in the other it is obtained through rotation of the tube line with which the plug is seated and fastened on the selected place.
In the cable plugs several problems may arise, such as when blasting charges are used, their deflagration produces gases generated in a closed chamber that are transformed into hydraulic pressure which at the same time causes a mechanical force. It may occur that the well fluid may penetrate inside the appliance thus avoiding its correct operation.
With the plug under consideration, as only the rubber has been swelled, it may be once more recuperated, which is not common with a conventinal plug because the latter has to be mechanically fastened and afterwards must be rotated and reinitiate the cycle, which is very costly.